During a few weeks around the summer solstice, the situation in the highest regions of the atmosphere can be ideal to form a rare kind of clouds. Invisible by day, these clouds can be lit by the sun when its beneath the horizon, showing up as noctilucent clouds.
For years I knew about these rare night shining clouds but I never really looked into it. I always thought these clouds were only visible above the polar circle, since really low temperatures would be necessary for these clouds to form. Why else were they called Polar Mesospheric Clouds also? But when a friend told me one evening, a few years back, there was a change to see it, I rushed outside and did see a glimpse of these elusive night shining clouds.
It was a one time observation for me, and although there were several other occasions in the years that followed, I never got a change to see the clouds. There was an occasion though, when I saw something that resembled these night shining clouds, better know as noctilucent clouds. But when I looked at the images I took that night, I never was convinced. Now I think these were another type of clouds (lower cirrus clouds), especially when I read more about it.
Although it is uncertain, scientists think extraterrestrial meteoric dust is the source of these clouds. But also volcanic dust is a real possibility. On these microscopic dust particles ice crystals are forming under specific conditions. These very small ice crystal, not more than 1/10,000 mm in diameter scatter the sunlight, making it visible for the naked eye in a darkened twilight sky.
These clouds are about 50 miles high in the sky, in the very dry, low pressure atmospheric region called mesopause. Under these circumstances ice can only form when temperatures drop below minus 123 degrees centigrade, which ironically only occur during summer.
Another problem scientists are faced with, it the origin of the water vapor. Since the mesopause is extremely dry, it is suggested the water vapor has its origin from reactions between methane and hydroxyl radicals. But due to the increased carbon dioxide concentrations, the mesosphere humidity is thought to be increase also, thus making noctilucent clouds to become more common.
Although I think a small understanding of the origin of these clouds can help in a quest for photographing it, I think it is more than enough for this article. The most important thing is perhaps knowing then these clouds can be visible, and where you should look.
Since the noctilucent clouds are op to 50 miles high in the sky, the sun will reflect in its ice crystals when it is set. You need to be between 50° and 65° latitudes to be able to see the noctilucent clouds, somewhere between mid May and mid August when you are at the Northern Hemisphere, and between mid November and mid February at the Southern Hemisphere. You should look to the northwest, low at the horizon, approximately one hour after sunset, turning towards northeast after midnight.
This year I almost forgot about these noctilucent clouds, until my girlfriend one night mentioned a weather forecast predicting a change of seeing these clouds. We were almost ready for bed, but I decided to take a look outside. And there, towards the darkening twilight sky, I recognized the clouds without a doubt. We rushed outside towards the park nearby and finally, after so many years, we had another opportunity to photograph these wonderful night shining clouds.
We witnessed a sky full of noctilucent clouds; bright and compressed low at the horizon, with the characteristic moving ripple and fiber structures, and open stretched higher in the sky. When the twilight faded into the night, the glowing clouds at the horizon became even brighter. We decided to drive to a nearby fen, to get out of the light invested city. There we enjoyed a spectacular display of noctilucent clouds while the evening fog crawled over the calm water, lit by the bright crescent moon.
When the night progressed we thought it was enough. How many pictures can you take from one location, with similar compositions? But when we drove back, I turned to a swimming lake for some more pictures. This was a rare occasion, with noctilucent clouds that were unparalleled, so we had to take the opportunity. It was long after midnight before we went to bed, but it was well worth it.
From my experience I can advise the following settings:
- Use a longer focal length, play with something between 50 mm and 200 mm
- Try to use a relatively fast shutter speed to see details in the clouds. Somewhere between 2 and 10 seconds
- Use an aperture that fits the scenery. I would suggest f/5,6 or f/4 for clouds above a far away background
- Choose the ISO value to get a good exposure; play around with shutter speed and ISO until it is to your liking, and don't be afraid of high ISO values
- Keep an eye on the histogram to get a proper exposure
- Use manual focusing (which can by tricky in the dark)
- For white balance I would suggest something between 3500K and 5000K, depending on the amount of artificial light
- Don't forget to turn of stabilization, use a timer or remote, and live view or mirror lockup in case of a DSLR
- And don't forget to enjoy the beauty of the noctilucent clouds
Have you seen noctilucent clouds and taking pictures of it? Please share your experience in the comment below.